Ordinary piston pumps and sliding valves have not been sufficiently successful to be widely used for molten aluminum and magnesium because of the abrasive oxides present in suspension in the melt. Sliding valves used to hold molten metal in a discharge pipe must have clearance to operate and this clearance allows leakage down the discharge pipe. Since the volume of leakage will vary with the time between cycles, the leakage will adversely affect the volume of the next pump cycle.
Gas displacement methods, with and without valves in the molten metal, are being used to meter molten metals, however the lack of positive control of metal displacement results in insufficient accuracy of metal charge size. Metal pumped by gas displacement pumps suffer from contamination from oxygen in the air and both oxygen and hydrogen in the humidity in the air. Expensive inert gases used to reduce contamination of the melt are generally not a practical economic substitute for compressed air.
An object of this invention is to provide pumping apparatus for accurately metering molten metal.
Another object of this invention is to maintain a molten metal discharge pipe full throughout the operation of the pumping apparatus.
An additional object of this invention is to provide pumping apparatus to dispense metal that has not been contaminated by air or humidity in the ambient air.
A further object of this invention is to provide a piston type displacement pumping apparatus with self cleaning characteristics.
A further object of this invention is to simplify the construction of pumping apparatus and its operation by using a stopper rod to hold molten metal in a discharge pipe and have it act as a valve to allow the pumping apparatus to take in a charge in an intake stroke while holding the metal in the discharge pipe.
Pumping apparatus in accordance with the invention comprises a submerged, or partially submerged, pump vessel or body equipped with a combined inlet and outlet valve on a stopper rod. The stopper rod serves to both hold metal in an outlet pipe connected to the vessel and also permit molten metal to be drawn through an inlet orifice into a pumping chamber of the vessel during an intake stroke of a piston. Lifting of the stopper rod closes the inlet orifice to the vessel and communicates the pumping chamber to an outlet orifice. Extending the piston into the vessel in a pump stroke forces metal through the now open outlet orifice and up the outlet pipe to dispense the molten metal in a measured amount. The amount of metal dispensed is dependent on the length of the stroke of the piston and other parameters. The length of the piston stroke may be mechanically adjusted or electronically adjusted as required to provide a desired volume of metal.